Various synthetic methods are available for preparing negatively substituted 2-aminothiophenes and 2-aminothiazoles, which are useful as intermediates for preparing azo dyes for textile fibers. (See, for example, Weaver and Shuttleworth, Dyes and Pigments, 3, 81-121 (1982).) Many of these procedures are complicated and laborious, with accompanying low yields. Often, the starting materials needed are not readily available and are expensive, thus rendering the desired negatively substituted 2-aminothiophenes and 2-aminothiazoles prohibitively expensive. Normally, to produce the most bathochromic colorants when diazotized and coupled, the 2-aminothiophenes must have negative groups in the 2,5-positions. These intermediate compounds are usually essentially colorless or are pale yellow in color as are the negatively substituted 2-aminothiazoles. Various colors from yellow to cyan can be produced by diazotizing and coupling the diazonium salts thus produced with appropriate couplers. It is very desirable to produce bathochromic blue shades and these are normally only possible when two very strongly electron withdrawing groups are in positions 2 and 5 of the intermediate thiophenes. None of these known intermediate negatively substituted 2-aminothiophenes or 2-aminothiazoles are useful as colorants.
It is known that 2-chloro-3-cyanomaleimide reacts with primary aromatic amines such as aniline to replace one of the hydrogens attached to the nitrogen, e.g. aniline reacts to give 2-anilino-3-cyanomaleimide. (Wiley et al., J. Am. Chem. Soc., 80, 138528 (1958)). ##STR1##
The compound thus produced has no significant color and has no utility as a colorant. Furthermore, since it has no primary amine present, the compound cannot be diazotized to produce a diazonium salt which is capable of being coupled to produce valuable azo colorants.
It is not expected, based on the prior art, that 2-aminothiophenes and 2-aminothiazoles, which contain primary amine groups, would react with 2-chloro-3-negatively substituted maleimides to give 5-negatively substituted 2-aminothiophenes and 2-aminothiazoles compounds useful as colorants and which have free primary amine groups capable of being diazotized to produce bathochromic azo dyes.
Various electron rich compounds are known to react with 2-chloro-3-cyanomaleimide to give colorants useful as colorants for textile fibers, but none have primary amine groups capable of being diazotized; no 2-aminothiophenes or 2-aminothiazoles are reacted. (See, for example, U.S. Pat. No. 3,096,339).